Why Do Dogs Eat Poop? The Gut Bacteria Theory Does Not Hold Up

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Quick Facts

This is our own research, not veterinary advice. For nearly every food there are many sources, and they do not always agree with each other. We check each claim against the veterinary and poison control sources, and we say plainly where they disagree. Even so, if you are in any doubt, contact a vet and do your own research before you feed anything to an animal in your care.

Dogs eat poop for reasons that are mostly behavioural, and the popular explanation that their gut lacks bacteria is not supported by the largest study on the subject. A survey of more than 3,000 owners found eaters and non-eaters did not differ in diet. Nothing you can buy makes a meaningful difference, which the numbers below show. Cleaning it up immediately is the only thing that reliably works, and a sudden change in an adult dog is worth a vet visit.

This is one of those topics where the popular explanation has outrun the evidence, and it is worth correcting because it changes what people do about it.

I have read the gut bacteria explanation online, that a dog eats excrement because its own gut is missing something and it is trying to top up. It sounds plausible. It is repeated constantly. And when you go looking for the study behind it, the largest piece of research on the question went the other way.

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Why Do Dogs Eat Poop? It Is Normal

The behaviour has a name, coprophagy, and it is defined as the eating of feces, which is normal behaviour among many animals rather than a disorder specific to dogs. Mother dogs clean up after their puppies, which is where most dogs first encounter it.

The best evidence we have comes from a 2018 study by the veterinary behaviourist Benjamin Hart and colleagues at the University of California, Davis, published in Veterinary Medicine and Science, which surveyed more than 3,000 dog owners. The finding that surprises people is how ordinary it is. About 16% of owners reported their dog eating stool more than six times, which was the study's threshold for being counted as a poop eater.

Just as interesting is what it was not linked to. There was no association with the dog's age, sex, neuter status, the age it was separated from its mother, how easy it was to house train, or the owner described problem behaviours. Whatever is going on, it is not a marker of a badly raised or badly behaved dog.

Some differences did show up. Eaters were more likely to live in multi-dog households, which may mean there is simply more available or that the behaviour is learned socially, and they were more likely to be described as greedy eaters who wolf their food down. And 85% of them preferred fresh stool, not more than two days old, which turns out to be a clue.

The Gut Bacteria Theory, Checked

This is the claim worth dealing with properly, because it is the one that leads people to buy things.

The theory is that a dog eats stool because its digestive system is missing something, whether that is gut bacteria, enzymes or nutrients, and it is supplementing by eating what has already been through another animal. It sounds reasonable, and it is wrong as a general explanation, at least according to the study above.

The key finding is that eaters and non-eaters did not differ in diet. If a missing nutrient or a gut deficiency were the cause, you would expect to see some difference in what the two groups were fed. The researchers did not find one. The study cannot rule out every subtle dietary difference, and the survey method has limits worth acknowledging, but it is the best evidence available and it points away from the deficiency explanation.

There is also a narrower version of the claim that is partly true, and it is worth separating from the broad one. A specific medical condition can cause coprophagy. Exocrine pancreatic insufficiency, where the pancreas does not produce enough digestive enzymes, is a genuine cause, and so is malabsorption. But that is a specific diagnosis with other symptoms attached, usually weight loss and a change in stool, and it is a different thing from the general idea that dogs eat poop because their guts are short of bacteria. A dog that stops eating is the opposite symptom and its own problem.

What the researchers proposed instead is behavioural and evolutionary. Their suggestion is that the behaviour may be inherited from wolves, where removing feces from the den area would have reduced the spread of parasites to the pack. That would explain why fresh stool is preferred, since fresh stool is the most likely to carry transmissible parasites. It is a hypothesis rather than a settled fact, and they say so, but it fits the evidence better than a nutritional one.

The Thing That Does Not Work

If you take one practical thing from this page, make it this. Products marketed to stop a dog eating poop do not work.

The same study asked owners to report on 11 commercial products, with names like Coproban, For-Bid, Dis-Taste, Deter and Potty Mouth. The reported success rate ranged from 0 to 2%. Owners overwhelmingly said they did not help. Behaviour modification and management approaches were also reported not to bring the behaviour to zero.

One of the study authors put it plainly, that there is no solution except to clean it up quickly. Scooping as soon as the dog goes makes the stool unavailable, and unavailable is the only state that reliably stops it. Owners who picked up most or all stools still reported it did not stop the behaviour entirely, but it reduces the opportunity, which is the most you can do.

The Risks, Without Overstating Them

It is worth being proportionate here. In most cases this is unpleasant rather than dangerous, and the dog is fine.

That said, there are real consequences. Eating stool can spread intestinal parasites and other diseases between animals, particularly in a multi-dog household or somewhere with lots of dogs. It can also cause an upset stomach and diarrhoea. Vets note that the outcome ranges from no trouble at all, to mild digestive upset, to the spread of disease depending on what was eaten.

On a sit, the practical version is straightforward. Keep picking up, keep an eye on the dog's stool for a couple of days afterwards, and mention it to the owner if it happens repeatedly, because they will want to know and may have a view on it.

When It Is Worth a Vet Visit

The behaviour is normal, but a change in it is not something to ignore.

If an adult dog that has never done this starts suddenly, or if the behaviour arrives alongside weight loss, a change in appetite, vomiting or a change in the stool itself, that is worth investigating rather than managing. Exocrine pancreatic insufficiency and malabsorption are both genuine possibilities and both are testable. Veterinary behaviourists make the same point: coprophagy can have medical underpinnings, and if there is any concern, a vet should be consulted.

If it is a puppy, the odds are it grows out of it, and the main job is managing the environment.

On a Sit, This Is a Management Problem

This comes up on sits more than people expect, and it is not a reflection on the dog or the owner.

The routine I would use is the boring one. Pick up immediately rather than leaving anything, and do it on every walk rather than assuming the owner's usual route is clear. If there are multiple dogs, watch the one most likely to do it, which is generally the one that eats fastest. And mention it to the owner rather than deciding it is your secret to keep, because they may already have a strategy and they will want to know if it has changed.

One caution for anyone looking after a dog in a public place. If your dog eats another dog's stool on a walk, that is a parasite risk rather than just a disgusting moment. The dog sitting guide covers the wider routine, and the pre-sit question list is worth checking against the owner's habits.

Where This Research Comes From

We are not vets. The claims here are traceable, and the main one rests on a single well designed study rather than a consensus.

The evidence on how common the behaviour is, what it is and is not linked to, the absence of a dietary difference, the fresh stool preference, the evolutionary hypothesis and the failure of commercial deterrents all come from Hart and colleagues, 2018, in Veterinary Medicine and Science. The accessible summary of the same study is Scientific American's write-up. The medical causes, including exocrine pancreatic insufficiency, are covered by PetMD.

Two honest limitations. First, this is a survey based study, which means it relies on owner report and cannot establish causation, only association. It is the largest thing we have on the question and it points clearly away from the nutritional explanation, but it is not the last word. Second, the wolf behaviour hypothesis is presented by the researchers as a suggestion rather than a finding, and we have described it that way rather than as settled.

If you are ever unsure, a vet beats every page on the internet, including this one.

Conclusion

Dogs eat poop, about one in six do it regularly, and it is not evidence of a bad diet, a bad owner or a broken gut. The gut bacteria explanation is the popular one and the study behind the question does not support it.

Nothing you can buy will fix it. Management is the whole answer, and a change in an adult dog is a vet question rather than a supplement one.

Caro and I have completed 20 house sits across 12 countries, driven 19,000km across Europe in our 1998 VW T4, and saved over $26,500 in accommodation costs over three years of house sitting.

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Frequently Asked Questions

• Why do dogs eat poop?

  Mostly for behavioural reasons, and the honest answer is that it is not fully explained. It is normal behaviour among many animals. The leading hypothesis is that it is inherited from wolves, where removing waste from the den reduced the spread of parasites.

• Is it true that dogs eat poop because their gut lacks bacteria?

  That theory is not supported by the largest study on the subject. A survey of over 3,000 owners found no difference in diet between dogs that eat stool and dogs that do not, which is what you would expect to see if a deficiency were the cause.

• Will a supplement stop my dog eating poop?

  Almost certainly not. The same study asked owners about 11 commercial products and the reported success rate ranged from 0 to 2%. Owners overwhelmingly said they did not help.

• Is eating poop dangerous for dogs?

  Usually unpleasant rather than dangerous, but not risk free. It can spread intestinal parasites and other diseases between animals, and it can cause digestive upset and diarrhoea. The outcome depends on what was eaten.

• Why does my dog only eat fresh poop?

  Because fresh stool is the most likely to carry transmissible parasites. In the study, 85% of poop eating dogs preferred stool that was less than two days old, which is one of the findings that supports the evolutionary explanation.

• Should I see a vet about it?

  Yes, if it starts suddenly in an adult dog or comes with other symptoms. Exocrine pancreatic insufficiency and malabsorption are genuine medical causes, and both are testable. If it has always happened and the dog is otherwise well, it is behavioural rather than medical.

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